A weighty issue: How much sugar is too much?

The damning evidence against sugar and its relationship to obesity arrived decades ago, with studies like one in which rats fed sugar, along with their standard diet, gained more weight, consumed more calories and got fatter than rats fed only standard rodent chow.

In one Tufts University study, published in the Journal of Nutrition 30 years ago, it didn’t matter what form of sugar — glucose, sucrose or fructose — the rats ate; they gained more weight than their control group comparisons who received only plain old chow.

Studies like that showed sugary diets induced obesity.

Animals on the sugary diets not only gained fat around their bellies, but they also had bigger appetites, consuming 15-per-cent more calories per day.

“Although the body must maintain a minimal level of blood sugar to avoid death, the brain is highly adept at recognizing rapidly dropping blood sugar and then responding with nervous signals leading to the release of hormones (cortisol and adrenalin) that raise blood sugar as well as activating brain appetite centres that provoke a strong urge to eat.”

“It suggests that overweight people tend to have highly variable blood sugar levels and that rapid drops in blood sugar in these people result in frequent, and often inappropriate, urges to eat. Likewise, when blood sugar is stabilized in these people, the frequency and intensity of appetite sensation decreases dramatically.”

A necessary evil

To be sure, sugar is not always villainous — it just becomes so when added to foods and refined, not to mention over-consumed.

People need nutrients for energy, cell maintenance, growth and repair. Carbohydrates, derived from sugars and starches, are as essential as water, fats and proteins.

Carbohydrates are a prime source of energy our bodies need to move. All carbs break down into glucose, but some metabolize faster than others. Simple carbs, which enter the bloodstream quickly, are derived from fruits and vegetables; complex carbs, which come from whole grain starches, are absorbed more gradually.

Brain cells called neurons and red blood cells depend on glucose; a shortage, Lyon says, can cause brain and other body systems to break down.

Glucose is an invaluable source of energy, but experts say its concentration in our blood should optimally be maintained at only about one gram per litre — or four to five grams in total. Four grams is about one teaspoon.

When we eat carbohydrates, there is a rapid rise in what is called our glycemic index, because sugar is rapidly absorbed into our intestines and then transported into our bloodstream. To respond, the pancreas releases insulin to control blood sugar levels. Insulin also helps transport glucose into the cells, and especially into the muscles. It stores glucose in the liver — the glucose distribution warehouse — and in muscles for future use and it helps convert extra glucose into fat.

The average body is said to have about 2,500 calories of carbohydrates in reserve — stored mostly in muscles and the liver — and another 100,000 calories stored in fat.

Dr. Daniel Metzger, a pediatric endocrinologist at B.C. Children’s Hospital, says sugars in beverages are probably the worst culprits in the obesity epidemic because they are consumed so fast and so plentifully.

“We can consume a lot of liquid carbs and not feel satiated,” he says. “Fructose (corn syrup) is a particularly bad player because it doesn’t set off any fullness alarms and it is also bad for the heart.”

Indeed, a study last year out of Princeton, published online by the journal Pharmacology, Biochemistry and Behavior, found that rats fed high-fructose corn syrup in addition to their regular diets gained significantly more weight than rats fed table sugar — even when the total amount of calories consumed was identical.

The concentration of high-fructose corn syrup in the water consumed by the rats was about half that of most sodas.

Long-term, rats fed high-fructose corn syrup for six months “showed characteristic signs of a dangerous condition known in humans as the metabolic syndrome, including abnormal weight gain, significant increases in circulating triglycerides and augmented fat deposition, especially visceral fat around the belly. Male rats in particular ballooned in size: Animals with access to high-fructose corn syrup gained 48 per cent more weight than those eating a normal diet.”

Restraint is key

In the hospital clinic where Metzger works, often with overweight kids and/or diabetics who have to monitor their intake of sugar, the message is delivered loud and clear: No juice, no pop. No liquid calories other than low-fat milk and no skipping of meals.

“I’ve seen two teenage patients recently who lost large amounts of weight by following these rules,” Metzger says. “They got more physical activity and they stopped drinking sugary drinks and they lost plenty of weight because of it.”

While the causes of childhood obesity are many, including lack of exercise and undesirable genetics, Metzger says “you can almost always identify places in the diet that can be fixed with overweight individuals.”

Lyon agrees with Metzger that added sugar — especially in the form of liquid candy — is a major factor in the rising rates of obesity, especially in children. Just one beverage can contain the equivalent of nine teaspoons of sugar. That means that if physical activity is not stepped up to compensate, a weight gain of seven kg will occur per year, based on a can of pop per day.

“Sugar-laden drinks like pop are probably the single biggest culprit. And fruit juice (even when no sugar has been added) is really no better as it is loaded with sugar and is easy to over-consume. Also, both table sugar and high fructose corn syrup contain significant amounts of fructose which, in higher amounts, promotes weight gain and may accelerate an overweight person’s progress toward diabetes.”

Lyon says refined, starchy foods — such as food made from white flour — digest rapidly into sugar, which then sends blood sugar up and down like a roller coaster.

“These big swings in blood sugar keep you craving snacks and make it likely that you will overeat. There is an ever-growing body of science that tells us that cutting calories is important to weight loss, but cutting way back on sugar and refined starchy foods is a very important strategy for long-term weight management.”

Recent studies looking at the effect that sugary, liquid calories have on weight have confirmed the benefits of cutting back on them.

In a study published in the Journal of Clinical Nutrition in 2009, researchers from Johns Hopkins examined the effect of beverages, including soft drinks, fruit drinks, artificially sweetened diet drinks, milk, alcohol and caffeinated drinks. At the start of the study, participants were typically drinking almost 400 calories a day in liquid calories. Sugar-sweetened drinks accounted for nearly 40 per cent of the liquid calories.

Of all the beverages, only the elimination of those that were sugar-sweetened made a significant difference in weight loss. A reduction of just one serving of such sugary drinks per day equated to weight loss of half a kilogram in six months.

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A weighty issue: How much sugar is too much?

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